The present invention relates to a display method and apparatus for an altitude display, and more particularly, to a display method and apparatus for measuring and displaying an absolute altitude.
In general, a multi-meter is a device for displaying information related to a vehicle driving state, for example, atmospheric pressure, absolute altitude, and driving direction. Such information is useful for a driver of a vehicle, especially for a driver who drives an SUV (Sports Utility Vehicle) that is driven in a variety of driving circumstances.
The multi-meter can function as an altitude display apparatus where a current altitude is displayed, and the current altitude can be displayed as absolute altitude or as relative altitude. Absolute altitude denotes an altitude relative to sea level.
In order to display the absolute altitude, the multi-meter detects an atmospheric pressure with a built-in pressure sensor, and calculates and displays the absolute altitude of a current driving position by comparing the detected atmospheric pressure with an average atmospheric pressure at sea level, which is approximately 1013 hPa (hectopascal).
However, there is a potential problem in this simple method of displaying absolute atmospheric pressure in that the atmospheric pressure not only depends on altitude but also on various factors such as weather and air temperature. As a result, atmospheric pressure at a same location sometimes changes more than 40 hPa according to the season and weather conditions.
Therefore, even for a place of which a real absolute altitude is higher than sea level, sometimes the calculated absolute altitude will show a negative value, which will cause confusion for a driver. Therefore, multi-meters of recently produced vehicles are usually preset to show a value of 0 instead of the calculated negative value.
However, this way of displaying also has a problem. If the pressure sensor produces a signal of 1033 hPa, the multi-meter will initially display xe2x80x9c0 mxe2x80x9d instead of the calculated xe2x80x9cxe2x88x92150 mxe2x80x9d. In this case, the display of xe2x80x9c0 mxe2x80x9d will continue until the vehicle goes up in altitude by more than 150 m from the initial altitude because the calculated absolute altitude will remain negative until that time. Therefore the driver will be confused because the multi-meter shows the same value even while the vehicle has moved up by quite a large altitude.
The present invention provides a display method and altitude display apparatus for displaying an absolute altitude in order to reduce operator confusion about a displayed absolute altitude, and therefore to enhance reliability and correctness of the absolute altitude displayed.
In a preferred embodiment of the present invention, an initial atmospheric pressure is detected, and an absolute altitude is calculated and displayed based on a pressure difference between the initial atmospheric pressure and a current atmospheric pressure if the detected initial atmospheric pressure is larger than a predetermined atmospheric pressure. The initial atmospheric pressure preferably can be detected when the ignition key of a vehicle is trans-positioned to an xe2x80x9cONxe2x80x9d state, that is, when electric power starts to be supplied to the altitude display apparatus, and the predetermined atmospheric pressure is about an average value of atmospheric pressure at sea level, for example, about 1013 hPa.
For the calculating and displaying the absolute altitude, the current atmospheric pressure is detected while a vehicle equipped with the multi-meter is running, a pressure difference between the current atmospheric pressure and the initial atmospheric pressure is calculated, an altitude difference is calculated based on the calculated pressure difference, and the calculated altitude difference is displayed as the absolute altitude. Prefereably, while displaying the calculated altitude difference, a value 0 is displayed when the calculated altitude difference is less than 0.
In a further aspect of the invention an altitude display apparatus comprises a pressure sensor, a control unit and a display unit. The pressure sensor provides pressure signals to the central unit, which calculates the pressure to be displayed and sends appropriate signals to the display unit to generate the display. The control unit is programmed to execute steps for calculating pressure to be displayed as described above.